Communications of the ACM
Know Your Steganographic Enemy
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In their review article "trends in Steganography" (Mar. 2014), ElŹbieta Zielińska et al. included a good survey of the history of data hiding and a comprehensive list of methods for inserting bits into cover objects but omitted an important actor from the scene—the enemy. In computer security, a system is secure only if it prevents the enemy from achieving certain specified goals. If the primary aim of steganography is to communicate covertly (as the article said correctly), then the enemy is someone—a "steganalyst"—who is able to monitor communications to detect covert communication. Such a scenario reflects reality in light of today's pervasive monitoring of the Internet by intelligence agencies and criminals.
Researchers would do well to identify new media that supports covert communication but only if they also prove it is not actually detectable by an enemy using the tools (such as statistical analysis and machine-learning algorithms) needed to unmask hidden data. I would not want a Communications reader to imagine steganographers forget they indeed have enemies, far from it. But few steganography methods survive long once researchers start trying to detect them through statistical methods. The only exceptions are ultra-low-bandwidth mechanisms that find perfectly random parts of the cover (where hiding is trivial) or highly refined methods that exploit coding theory and distortion minimization applied (at least in recent years) to image steganography.
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